Telephone system



Nov. 17, 1931. w. B. STRICKLER 1,332,263

TELEPHQNE SYSTEM Original Filed May 27, 1927 2 Sheets-Sheet l IlHl- //v v/v r01? WB. Sm/cm. ER

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A 7'7'0/PNE Y 2 Sheets-Sheet 2 g 3L."- m d l H- =z=' v I 5 I AA flAll HVV'YV i HIIHI xi q i) j //v|//v7'0/? WflSTR/CKLER ATTORNEY W. B. STRICKLER TELEPHONE SYSTEM Original Filed May 27. 1927 Nov. 17, 1931.

Patented Nov. 17, 1931 UNITED STATES.

WALTER B; STRICKLER, or EASTQORAINGE, nnwanns nmnssrenon To BELL TELEPHONE LABORATORIES, INCORPORATED, or nnwvonxyn. Y., A conrone'rron on NEW" YORK Original application filed May 27, 1927, SeriaIN 19 This invention relates to telephone systems, and its object is to secure improvements in cord circuits for use in private branch. exchange systems.

This application is a division of my application, Serial No. 194,576, filed May 27, 1927, on which patent 1,747,849 was granted Feb. 18, 1930. This patent discloses a cord circuit for private branch exchange systems in whlch the tip and ring conductors'between the two plugs arenormally connected respectively to ground and battery through impedance coils, means whereby when the cord circuit 1s used for establishing a connection between two local subscribers lines it is converted into a bridged impedance battery feed cord, and whereby when the cord is used for establishing a connection between a local exchange subscribers line and a central oflice trunk t is converted to a circuit through which the battery is fed from the central office source.

A feature of the present invention is a cord circuit ofthis general type in which an inductive low resistance bridge is placed across the tip, and ring conductors when a connection is established thereby between a trunk from a central oflice and a private branch exchange subscribers line, and in which, when the private branch exchange subscriber answers such a call, a non-inductive highresist-ance bridge is added to the low resistance bridge. This is for the purpose of preventing false momentary release of the superv sory relay at the central office when the private branch exchange subscriber hangs up, preliminary to the release of the connection or when the private branch exchange subscriber wishes to recall the privatebranch exchange operator.

The invention is applicable to cord clrcuits for interconnecting two private branch exchange subscribers lines and for interconnecting a private branch exchange subscribers line with a central oflice trunk, and by means of which dialing impulses may be transmitted over such a trunk to select a subscribers line through switches at an autor. matic central oifice;

1929. Serial No. 405,299.

TELEPHONE sYs'rnM 4,576. Divided I and this application filed November 7,

2 and 3represent a preferredform of circuit arrangement embodying the features of this invention. r F ig. 1 shows a private branch exchange cord clrcuit and a manual private branch exchange subscribers line;

12 shows another manual private branch exchange subscribers line; and" vFig. 3 shows jthe'equipment of a trunk line outgoing from a private branch exchange and endingin a manual central office. e Referring now tothe drawings, descriptions will be made: First, ofthe operations ofthe circuits shown when a connectionis established between the private branch exchange subscribers lines 1 and 100 through the cord circuit 2; second, of the operations taking place when a connection is established between the private branch exchange subscribers line 1 and the trunk 101 through the I I cord circuit 2; and1third, of the operations takingplace when a connection is established from a central office over trunk line 101to the private'branch exchange subscribers line 1 through cord circuit 2. 5 I

If it is assumed then that the private branch exchange subscr iber of line 1 desires toycommunicate with the privatetbranch exchange subscriber of line 100, he will initiate a connection by lifting his receiver from the hook and thus cause the lamp 3to be lighted in the usual manner. In answering this call, the private branch exchangeoperator inserts plug 4 into jack 5, thus causing the operation of relay 6 over an obvious circuit to extinguish lamp 3. The establishing of this .connection also closes a circuit for the operation of relay 8 as follows: Battery through the lower winding of relay 8, lower inner armature andback contact of relay 10, sleeve terminals of plug 1 and jack 5, right-hand armature. and front. contact or relay 6 to ground. The operation ofrelay 8 closes an obvious circuit for the lighting of supervisory lamp 13 and'also connects batteryand ground through the retardation coil 14 to the tip and ring conductors of the calling subscribers line. This circuit may be traced frombattery, through. the right-hand winding'of retardation coil 14, lower armature III p as jack 102 of line and front contact of relay 8, lower outer normally made contacts of key .15, right-hand winding of supervisory relay 16, lower normally made contacts of ringing key 17, ring terminals of plug 4 and jack 5 through the calling subscribers loop, tip terminals of jack 5 and plug 4, upper normally made contactsof ringing key 17 ,left-hand winding This circuit supplies talking battery for. the

calling subscriber.

The talking and dialing key 19 is now operated to connect the 'operators telephone circuit and dialing equipment 23 to the cord 2. The operation of this key connects the operators telephone set and dial to the cord over a circuit as follows :battery, lower wind" ing of relay 24, lower outer armature of back contact of relay 10, lower inner made con tacts of key 19, lower make-before-break contacts of relay 25, primary windings of repeating coil 66,- pulsing contacts of. dial 2?, upper make-hefore-break contacts of relay 25, upper inner made contacts of key 19,11pper armature and back contact of relay 10, upper winding of relay 24 to ground. A circuit is also closed for the operators receiver 28 in parallel with'the lower primary winding of repeating coil 26 through a-condenser 31and the upper armature and back contact of relay 32, and lower outermade contacts of key'1'9.

Relay 24 operates in this circuit but performs no useful function at this time.

" The operator now asks the calling subscriber for the number wanted and if another private branch exchange subscriber is wanted, such as the subscriber of line 100, the operatorwill perform the usual busy test by touching the tip of'plug 33 to the sleeve of If line 100 is busy, ground will be connected to the sleeve of jack 102 due to the operation of relay 103. In this case, the operator will receive a click in the receiver 28 due to the fact that direct ground will be connected to one side of the condenser 31 through the upper primary winding of re- '34, tip terminalof plug 33, sleeve terminal of jack 102 to ground at the left-hand armature and front contact of relay 103.

On the other hand, if line 100 is idle relay" 103 will not-be operated at this time. Hence, the operator will insert plug. 33in jack 102 and ring the subscriber of line 100 by operating ringing key 34. WVhen the called subscriber'answers and the operator removes-her'telephone set and dialing equipment from the line by releasing key 19, the

connection between the subscriber of line 1 and the subscriber of line 100 will be ready for conversation. It should be noted that the talking battery as hereinbefore described for the calling subscriberof line 1 is supplied through retardation coil 14, while the talking battery for the called subscribers line will now be supplied as follows: Battery, lower windingof relay 24, lower. outer armature and back contact of relay 10, lower inner normally made contacts of key 19, lower middle normally made contacts of key 15, lower normally made contacts of ringing key .34, ring terminals of plug 33 and jack 102, the called subscribers loop back to the tip'terminals'of jack 102 and plug 33, upper normally made contacts of rin ing key 34, middle upper normally made contacts of key 15,

upper inner normally madecontacts of key 19, upper armature and back contact of-relay 10, upper winding 'of relay .24 to ground.

Relay 24 in operating opens the circuit for lamp 13 and the extinguishing of this lamp indicates to the operatorthat the called subscriber had answered thecall. These two con- 5 nectlons to talking battery are joined by means ofcondc-nsers 37 and 38, to complete the circuits for conversation between the two subscribers. i

If the calling subscriber releases by replacmghis receiver on the hook, relay 16 is released and lamp 36 is lighted over the sleeve circuit-.to indicate that disconnection is desired and when the operator removes the cord from the connection, relay 8 is released to return the circuit to normal. If the called is desired.

If a connection is desired from the private therebv lighted to indicate that disconnect-ion branchexchange subscriber of line 1 to a centraloflice over a trunk such as 101' and to a wanted subscribers line in this otfice the operatlons of the cord clrcuit 2 are practically identical with the operations thereof when used for connecting two private branch exchange subscribers, except that in this case when plug 33 1s lnserted in jack 105a circuit through the sleeve terminals of plug 33 and jack 105 will be completedfor the operation of relays 106 and 10 as follows:

Battery, winding of relay 106, upper outer closed contacts of jack 105, sleeve terminals of jack 105 and plug 33, winding ofrelay 10 to ground. The operation of relay 106 closes a connection to relay 1 07 and this relay operates as hereinafter described and for a purpose as will presently be set forth. Relay 10 in operating opens the energizing circuit for relay 8 at its lower innerarmature andback contact so that this relay wilLnowrelease and remove the battery and ground supplied through the; windings of retardation coil. 14

trunk.

for the calling-subscribers line; Relay 10 also removes battery and ground supplied through the winding of'relay 24 toward the The operation of relay 10 and the release of relay 8 will now-connect the plugs 33 and 4 together without. battery connections. It should be noted that relay 16 is now operated since a circuit isestablished through the cord and the Calling. subscribers loop from battery and ground through the windings of relay 107, which is operatedas hereinafter described in connectionwith a call to a manual central oflice overtrunk 101. Operation of relay 16 causes relay 24 to reoperate over a circuit from battery,-lower winding of relay 24, lower outer armature and front contact of relay 10, upper winding of relay 8, upper inner normally made contacts of key 15,-armature and front :contact of relay 16 to ground at relay 6. The operation of relays 10 and 24 establishes a bridge through the inductive low resistance middle winding of retardation coil 14 and non-inductive high resistance 40 across the tip andring conductors of the cord,through'the upper armature and front contactof relay 10 fora purpose as hereinafter described. This bridge will remain in the circuit as long as the connection between the two subscribers remains intact. Thepurposeof including the high resistance in the'bridge is to improve thetransmission characteristics for the talking current between the subscribers as is well known inthe art.

The circuit for the operators telephone set and dialingequipment in this case extends, for the tip conductors from the upper secondary winding of repeating coil 26- to the tip conductor through the pulsing contacts of dial 27, upper. outer made contacts of key 19,

upper middle normal contacts'of key 15,.up

per normally made contacts of ringing key 34 to the tip terminal of plug 33,:while the connection to the tip terminal'of plug 4 extends through the upper make-before-break contacts of relay 25, upper inner made contacts of key 19, upper outer armature and back contact of relay 8, upper outer normally made contacts of key 15, left-hand winding of relay 16 and upper normally made contacts of ringing key 17 to plug 4. The connection for the ring conductors extends through the lower secondary winding of repeating coil 26' and the operators receiver 28 in parallel through the lower outer made contacts of key 19, middle lower normally made contacts of key 15, lower normally made contacts of ringing key-34 to the ring terminal of plug 83, while the connection-to the ring terminal of plug 4 extends through the lower make-before-break contacts of relay 25, inner lower made contacts of key 19, lower armaturev and back contact of relay 8, lowersouter-normally made-contacts of key 15, right hand winding of relay16 and lower normally made contactsof key 17-to plug4. l

If the distant end of the trunk 101 ter minates at a manual central oifice it will be equipped withthe apparatus shown in Fig. 0. Assuming'that the privateIbranch exchange operator. has established a'connection to a manual central otlice, the fact that the tip and ring conductors are bridged throughthe private branch exchange operators telephone set and through thecalling subscribers loop I and that relay 106 is-operated, causes a circuit to be established for the operation of the line relay 107 This'relay operates and causes lamp 108 to be lighted to indicate to the operator at the central ofiice that a connection is desired over this trunk. The operator answers this call by inserting a plug into jack 109 and thuscauses relay 110 to be operated over the usual sleevecircuitto disconnect relay 107 and extinguish lamp 108. The tip and ringconductorsare now connected through to the battery and ground in the usual cord and central oi'iice operators telephone setin .be supplied from the operators cord at the central ofiice. W i

If the calling subscriber disconnects after the conversation is finished relay 16 will be released.- Thisrelay in releasing completes the circuit forythe supervisory lamp 36 to indicate to the private branch exchange operator that the calling subscriber has disconnected. It should be noted that on the release of relay 16 the circuit for relay 24 is opened causing this relay to release. The high noninductive resistance40 in'the bridge across the tip and ring conductors is thereby short circuited to prevent the release of the connection tothe called subscriber by maintaining, for example, the usual supervisory relay in the centraloiiice operators cord operated.

It should, however, be observed from the time the receiver is replaced and the relay 24 is released, the highresistance bridge is the only bridge in the circuit, and while this period is short, false release of the supervisory relay at the central ofiice may occur at this time. It is therefore essential that although the calling subscriber may have hung up the receiver for the purposeof releasing the connection, the supervisory relay at the central office must beheld operated until the private branch exchange operator. actual-1y removes the cord in response to the disconnect signal. To prevent such false signaling the high.resistance 40 has been made non-inductive so that the sudden removal of the low resistance bridge by the subscriber hanging up his receiver and the replacing of the high resistance bridge will not cause any sudden momentary decrease in the current through the line'prior to-the'relcase of relay 24 when the new low resistance bridge comprising the middle winding of coil 14 is substituted." Had this high resistance 40 beenof the inductive type the momentary decrease in the current caused thereby, when the low resistance bridge through the subscribers loop was removed, may have had the effect of momentary releasing the supervisory relay at the central ofiice to give a false signal indication. When the operator removes the cord from the connection the-supervisory relay at the central oflice operators cord is released to indicate to this operator that the calling subscriber has hung up his receiver and that the connection has been broken down by the private branch exchange operator.

It may further be observed in this connection that the calling subscriber. may wish to recall the private branch exchange operator and it is of course equally essential that the condition at the central oflice should not be disturbed under these circumstances. To call this operator the subscriber will alternately replace and remove his receiver a number of times. This will cause relay 16 to be alternately released and operate to fiashsignal 36. Relay 24 will also be alternatelyreleased and operate in unison with relay 16 and consequently remove and replace the high resistance 40 in the bridge across the line. Vere it not for the fact that this resistance is of the non-inductive type false release of the supervisory relay at the central office may occur during the recalling procedure.

If the trunk 101 is connected to automatic machine switching apparatus in an automatic central oflice insteado'f to a manual central oflice, the seizure of this trunk by cord 2 will, due to the fact that the middle winding of retardation coil 14 and resistance 40 or the operators telephone set and dialing equip ment are bridged across the tip and ring conductors, cause operations to take place at the central office to connect the usual pulsing relay for controlling the extension of a connection automatically to a wanted subscriber. In this case, the private branch exchange operator dials the number of the wanted subscriber on dial 27 and causes the switches at the central office to complete the connection. As this invention is not concerned with the operation of such automaticequipments at the central ofice it has not been shown or described. I r

The privatebranch exchange operator in moving his dial 27 from normal 'closesa circuit through the off-normal contacts for the operation of relay 32. 1 Theoperation of this relay opens the circuit through the receiver 28 at the upper .armature and back contact i and closes a circuit at this upperarmatu re and its front contact through a resistance 43 in parallel'with the secondary windings of re peatingcoil 26. The resistance 43, inserted in parallel with the secondary of the repeating coil 26 performs 'no useful function at this time, but its use later in this circuit will be described hereinafter. The operation of relay 32 causes a circuit to be closed for the operation of relay 44 over a circuit as follows battery, winding of relay 44, lower armature and front contact of relay 32, ofi-normal contacts of dial 27 to ground. Relay 44 in operating closes an obvious locking circuit for relay 32 and closesfat its lower outer armature and front contact a shunt for the resist ance 43 so that on the return of the dial 27 to normal the dialing circuit will be free from all impedances duringdialing. The operation of relay 44 also closes a circuit for the operation of relay. 25 as follows: Battery, winding ofrrelay 25, inner lower armature andfronticontacts of relay 44 to ground. Helay 25 in operating splits the connection between plugs 4 and 33 at the make before-break contacts ofthis relay and connects battery and ground through the windings of relay 4.6 and the upper .and lower armatures and front contacts of relay 25 to. the tip and ring conductors leading. towards. plug 4. Relay 46 is thereby operated through the calling subscribers loop and provides a locking circuit for relay 25.. This relay also closes connections at its upper and lower inner armatures and front contacts through condensers r 49 and 48'to complete a circuit to the operators telephone set so that the operator may be able to talk tothe calling subscriber in case the talking and'dialing key is not immediately returned after dialing. The tip' and ring-conductors leading towards plug 33 are, of. course, still connected through-the pulsing contacts of dial 27. This dialing circuitrinay be traced-to the'tip and ring conductors of trunk lOl and the machine switchmgapparatus at the distant central office as follows: from the dial contacts of dial 2?, upper outer made contacts of key 19, upper middle normally made contacts ofkey 15,

upper normally made contacts of key 34, ring terminals of. plugv 33 and jack. 105 through the pulse relay or pulsingrelay at the central ofiice, back through the ring terminals of jack 105 and plug 33, lower normally made contacts of key 34, middle lower normally made contacts of key'1'5, inner lower made contacts of key 19, back through the pulsing contacts'of the dial27.

It will be noted that thebridge'across the tip and ringcondu'ctors" of the middle windapparatus may now take place.

ing of retardation coil 14 and resistance 40 is pulses by the secondary windings of repeat-.

ing coil 26. The release of dial 27 to normal will no-w'open the connection for the tip'and ring conductors towards the central oiiice in accordance with the number selected and the central ofliceapparatus are thereby advanced to select the first digit.

When the dial returns to normal the OE- normal contacts open and cause the release of relays 32 and 44. These relays areslow in releasing, but relay 32 is slower than relay 44, so that the resistance 43 will remain bridged across the secondary of the repeating. coil 26, a short period after the shunt therefor is removed by the release of relay 44. The purpose of the momentary insertion of the resistance 43 across the tip and ringconductors at this time is to prevent false operation of the central office pulsing relays betweendigits, that is, to prevent the secondary of the repeating. coil 26-from causing a false pulse indication to the centralotfice appara tus due to the high impedance of this coil. In other words, the non-inductive resistance 43 remains in circuit until the current through the secondary windings of repeating coil 26 is sufiiciently built up to hold the central oflice apparatus actuated through the bridge formed by thesewindings. It will be notedthat the release of relay l4 closes connections through the condensers 47 and 48 betweenthe calling subscribers line and the secondary windings of the repeating coil 26 and the release of relay 32 reinserts the receiver in parallel with the lower primary. winding of repeating coil 26 so that the conversation between the operator and the calling subscriber may takeplace in case the dialing key is not immediately released after dialing.

\Nhen the desired number has been selected by the private branch exchange operator she will remove her telephone set and dialing equipment from cord 2 by releasing key 19' and. conversation between the. calling subscriber through the automatic central oflice When key 19xwas returned to normal it should be observed that the bridge through the middle winding of retardation coil 14 and resistanceAO was reconnected across the tipandring conductors. The connection for the tip and ring conductors from plugs 4 to 33 maybe traced as follows: From tip terminal of plug 4, upper normally made contacts of key 17, right-hand winding of relay 16,

upper outer normally made contactsof key 15, upon outer armature and back contact of relay-24, upper inner normally made contacts of'key19, upper middle normally madecon tacts of key 15, upper normally made contacts of key 34 to tip terminal of plug 33, while the circuit for the ring conductor may be traced from ring terminal of plug-4, lowernormally.

made contacts of key 17,1eft-hand winding of relay 16, lower outer normally made contacts of key 15, lower armature and back contact of relay 8, lower inner normally made contacts of key 19, middlelower normally made contacts of key 15, lower normally made contacts of key 34: to the ring terminal of plug 33. v w

It will be noted that the windings of the ring the wanted subscriber as he is automatically called through the automatic equipment 7 of the central ofiice as is well known in the.

If a call is incoming over trunk 101' from either a manual or automatic central ofiice and the cord circuit shown in Fig. 1'is used,

the relay 111 will be operatedjby ringing current therefrom.

nected at the lower armature and back contact of relay 106. The private branch exchange operator, in this case will answer-the call by inserting plug 33 into jack 105 and Obvious circuits are; thereby closed for the lighting of. lamp1112- and the operation of relay 113. Relay 111 islocked in operated position from ground con so usual supervisory relay 16 are connected in;

It should be understood that the V the operationof'the circuits for establish-- I ing a connection toa wanted'subscriber in the private branch exchange are identical with the operations as hereinbefore described in connection witha call originatingiat the private branch exchange except thatinthis case relay 8 will not operate due to the fact that therelay 10 is already operated before plug 4 is inserted into the jack of the wanted subscribers line. Relay'106 operates with relay 10 causing the release of relay 111, the

extinguishing of lamp 112 :and release of relay 113. Relay 113 is slow in releasing so that a circuit through the non-inductive resistance 114 will be closed across the tip and ring conductors of the trunk 101; This bridge will trip the ringing at the central office in a manner wellknown in the art.

. VVhenrelay lO'operates it should be noted that the inductive low resistance bridge through the middle winding of retardation coil 14 willbe established across the tip and ring conductors of tlie'cord. The circuit "forthis bridge may be traced from the tip conductorcmiddleupper contacts of key 15, upper normal contacts of key 19, upper armature and front contact of relay 10,middle WlIldlIlg of retardation coil 14, inner lower armature and back contact of relay 24,

lower normal contacts of key 19, middle low-' 7 er contacts of key to the ring conductor.

This inductive low resistance bridge causes the supervisory relay in the cord circuit at the central oflice to be operated to extinguish the usual supervisory signal. The

cord circuit at the central ofiice has not been shown as it is Well-known in the art how .thissignal is actuated and that an inductive low resistance bridge has to be provided "across the tip and ring conductors for the trunk in order that sufiicient current will be supplied for the operation of the super visory relay, \Vhen the called private branch eXchange subscriber answers the call and completes a low resistance loop across the tip and ring conductors by removal of the receiver from the switchhook, relay 16 is operated and closes a circuit from the ground on the sleeve of .plug 4 through the armature and front contact of relay 16, upper inner normal contactsof key 15, the upper winding of relay 8, lower outer armature and front contact of relay 10, lower wind ing of relay 24 to battery. Relay 2% operates and opens the shunt around the 11011-l11ClUC- tive high resistance 40 so thatthe bridge across the tip and ring conductors of the cord will now extend through this non-inductive high resistance 40in addition to the inductive low resistance middle Winding of V ofiice 'Whenthe bridgeris still in the circuit.

7 circuit arrangements without departing from the spirit of the invention and that the above disclosures should'only be taken as illustraretardation coil 1a. It'is. however. as described above, important that this high resistance bridge should be of such nature as to prevent a momentary release of the supervisory relay in the cord'circuit at the central tive of an application of the invent-ion.

WVhat is claimed is: 1. In a telephone system, two lines, a link circuit for connecting said lines, means responsive to the establishing of such a connec tion for placing a low resistance bridge across the talking conductors of said link circuit, and means for later including a noninductive high resistance in said bridge. 7

V 2, Ina telephone system, two linessa link circuit for connecting said lines, ineans r'esponsive to the establishing of said connectionfor placing an inductive resistance" bridge" acro'ssgthe talking conductorsof said link circuit, and means forlater including a non-inductive resistance in said bridge.

3; In a telephone system, a called subscribers line, a trunkline, a cord circut for estab connection for placing an inductive low re sistance bridge across the tip and ring con-1 'd-uctors of said cord circuit, and means re-.

sponsive to the subscriber ansii 'ering a call for including in said bridge a non-inductive high resistance. I

5. In a telephone system, a called subscribersline,a trunk line, a cord circuit for establishing a connection from said trunk line to said called subscribers line, means responsive to the establishing of said connection for placing an inductive low resistance bridge across the talking conductors of said cord circuit, and meansresponsive tothe called subscriber answering a call for including in said bridge anon-inductive high resistance. 1 6. In a telephone system, two lines, alink circuit for'connecting said lines, means responsive to the establishing of such a connection for placing a direct current resistance bridge across the talking conductors of said link circuit, and means'for later including a non-inductive high resistance in said bridge. 7. Ina telephone system, two lines, a link circuit for connecting said lines, means responsive to the establishing of such a connection for placing a direct current low inductive resistance bridge across the talking conductors of said link circuit, and means for later including a non-inductive resistance in said bridge.

8. In a a telephone system, a called subscribers line, a trunk line, a cord circuit for establishing a connection from said trunk called subscriber answering a call, andmeans responsive to the actuation oi? saidsupervisory relay for includi a non-inductive high resistance in said bridge.

In witness whereof, I hereunto subscribe my name this 4th day of November. 1929.

" WALTER B. STRICKLER. 

